During the two years this project has been funded, considerable progress has been made towards the development of a general computer model that will adequately simulate the behavior of animals under choice procedures. Funding is requested for three more years to (1) refine computer models already developed by the PI to simulate the performance of animals responding under concurrent schedules of reinforcement; (2) extend the models to procedures that involve choice among more than two behavior alternatives, and (3) create realistic screen graphics of a laboratory animal responding in a Skinner box under schedules of reinforcement. The graphics program will be interfaced with the computer models of schedule controlled responding to yield interactive on-screen simulations of the behaving animal (the "virtual" rat). The program will permit the user to alter the animal's behavior by manipulating the consequences of its responses or by altering some other aspects of the virtual rat's environment. The user, for example, will be able to shape the virtual rat to press a lever by reinforcing successive approximations to the desired behavior, or he/she could extinguish established responding by withholding reinforcement, or could increase the rate of lever pressing by reducing the force required to operate the lever. It is anticipated that a virtual rat graphics program with the associated computer models of schedule controlled responding could be used to substitute some of the time consuming, and expensive laboratory exercises involving rats or pigeons that are usually part of college courses on Conditioning and Learning, Experimental Psychology, etc.